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Logic Schematic "Four Counter" version of the EC-132 Calculator June, 1965
This is a logic-level schematic for the Four-Counter version of the
Friden EC-132 electronic
calculator. The Four-Counter version of the EC-132 was an early
implementation, with calculators after serial #3901 switching
to the Three Counter architecture, eliminating the B counter and its
control logic to simplify the machine.
The schematic includes all of the logic for the calculator
at the gate and flip-flop level. The schematic includes only the logic
circuitry located on the plug-in circuit boards, and does not include the
power supply, details of the write driver and read amplifier for the
delay line, as well as details of aspects of the CRT drive and deflection
Given that the EC-132's logic is implemented entirely with discrete components
the schematic uses unusual symbology and nomenclature to designate
the logic elements. The general
logic function is the OR gate, which is shown in the schematic as a box
with an "O" at the top center. Boxes with an "I" in the top center are
inverters. Boxes with "EF" are transistor emitter follower circuits, used
on the output of gates to allow higher fanout capacity for gates that need
to drive many other gate inputs. Boxes that are divided in half by a
horizontal line represent flip flops. Other small boxes with diamond-shaped
symbols on inputs are called AC gates, which operate on logic level transitions
rather high or low states. The logic design is well described in the
EC-132 Temporary Service
Manual, as well as in the
EC-130 Service Manual.
This schematic can be used in conjunction with the Four Counter
Friden 132 Master Design Document
(MDD, a.k.a. Computer Printout) to determine the actual components used
for each logic gate and flip flop.
Any re-distribution of this document, printed or electronic,
must include the watermark indicating its source as the Old Calculator Museum. Thank you.
Logic Schematic for Friden EC-132 Electronic Calculator
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